Inhibition of in vitro growth of Plasmodium falciparum by purified antimalarial human IgG antibodies. Isolation of target antigens from culture supernatants.

In the search for candidate molecules for a malaria vaccine the in vitro inhibition of Plasmodium falciparum cultures by polyclonal or monoclonal antibodies has become a major tool. In the present study antigens identical to antigens circulating in plasma during attacks of malaria have been isolated from supernatants of P. falciparum cultures and used for immunoadsorbent purification of IgG antibodies from a pool of human immune serum collected in Liberia. Approximately 50% growth inhibition of three different P. falciparum isolates from Africa was obtained with the affinity-purified antibodies at a concentration of 25 micrograms ml-1 culture medium after 48 h of incubation. The target antigen/antigens for the protective antibodies have been partly characterized by radiolabelling, polyacrylamide gel electrophoresis and autoradiography but have not yet been identified unequivocally. However, the results indicate that one or more of the easily isolated antigens from the supernatant of P. falciparum cultures could be used in a malaria vaccine. The results also indicate that antigenic differences between strains from geographically disparate areas may not constrain the development of such a vaccine.